Polyurethane is well known as a base product for the manufacture of rigid foams which are used widely as insulators in refrigerators and freezers, in insulating panels for buildings, and for the refrigeration industry, in sheets for insulating transportation means, tanks, pipes, and even for the production of high-density rigid foams for furniture or for technical products in general.
Polyurethane is also well known as a base product for the manufacture of flexible or semiflexible foams which are used widely as cushions and mattresses in the furnishing industry, and as padding in seats, arm-rest, bumpers etc. in the car industry, where it is often used with the RIM-RRIM technology.
Polyurethane foam is produced by the intimate mixing and reaction of two liquid products, an isocyanate component, usually crude MDI, and a polyol component which contains all or some of the following products in a homogeneous mixture:
polyols -- reactive products of suitable molecular weight for reacting with the isocyanate to form a rigid, flexible or semiflexible product; PA1 catalysts -- generally tertiary amines or potassium, tin or lead salts, which regulate the reaction rate; PA1 surfactants -- which affect the surface tension and regulate the formation of the foam; PA1 water which reacts with the isocyanate to produce carbon dioxide which acts as an expander; PA1 flame-retardants which regulate the behaviour of the foam with respect to fire; PA1 expanding agents, that is, low-boiling products which regulate the expansion of the foam; PA1 various additives such as fillers, dyes and pigments for various applications. PA1 continuous: the reactive polyurethane mixture is cast onto a conveyor belt, is restrained laterally, and is allowed to expand freely until the product has hardened; after curing, the product is trimmed and cut into sheets; PA1 discontinuous: the reactive mixture is poured into container tanks and is left to expand freely until a hard block of foam is formed; after curing it is trimmed and cut into sheets. PA1 continuous: the reactive mixture is cast onto various paper, metal or glass cloth coverings where it expands to fit the coverings, forming a covered rigid foam panel; the panel is then trimmed and cut to size; PA1 discontinuous: the reactive mixture is cast into moulds or presses in which the coverings are positioned and is left to expand until it fills them completely, adhering to the coverings and thus creating covered panels.
The polyol component and the isocyanate component are thermostatically controlled, metered, mixed and poured by means of suitable machines.
Various formulations of the polyol component are used to produce different types of rigid, flexible or semiflexible foams by various processes, some of which are described by way of example below.